target/arm: Allow VFP and Neon to be disabled via a CPU property

Allow VFP and neon to be disabled via a CPU property. As with
the "pmu" property, we only allow these features to be removed
from CPUs which have it by default, not added to CPUs which
don't have it.

The primary motivation here is to be able to optionally
create Cortex-M33 CPUs with no FPU, but we provide switches
for both VFP and Neon because the two interact:
 * AArch64 can't have one without the other
 * Some ID register fields only change if both are disabled

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20190517174046.11146-2-peter.maydell@linaro.org

target/arm/cpu.h

@@ -786,6 +786,10 @@ struct ARMCPU {
     bool has_el3;
     /* CPU has PMU (Performance Monitor Unit) */
     bool has_pmu;
+    /* CPU has VFP */
+    bool has_vfp;
+    /* CPU has Neon */
+    bool has_neon;
 
     /* CPU has memory protection unit */
     bool has_mpu;